With the development of communications technologies, a data transmission rate becomes increasingly high. Correspondingly, bandwidth required for data transmission also becomes increasingly high. However, in a current frequency spectrum distribution condition, it is extremely hard to directly obtain a relatively wide contiguous frequency spectrum. Therefore, it is an inevitable communications development trend to aggregate multiple frequency spectrum fragments for data transmission. In a current Long Term Evolution (Long Term Evolution, LTE) standard, a requirement for supporting double-carrier aggregation is proposed, and a possibility of five-carrier aggregation is defined. Because aggregated carriers may cross a relatively wide frequency band, it is extremely hard to get all carriers together as a single frequency band for processing. If signals carried on all the carriers are separately moved to a baseband to perform sampling and demodulation, each carrier needs a radio frequency channel. With an increase in a quantity of aggregated carriers, a quantity of radio frequency channels also increases accordingly, which causes corresponding increases in circuit complexity and power consumption.
To resolve the foregoing technical problem, in the prior art, frequency mixing is performed on a periodic sequence (also referred to as a multi-tone local oscillator signal, multi-tone local oscillator signal) having a comb frequency spectrum and a multiband signal including multiple scattered narrowband signals, so that aliasing of all the scattered narrowband signals included in the multiband signal is performed on the baseband, and sampling points of all the narrowband signals are separated according to an algorithm. By using the foregoing technical solution, the multiband signal may be processed by using one or several radio frequency channels, which significantly reduces the circuit complexity and the power consumption.
In the existing various multi-tone local oscillator signal generating methods, a method for generating a multi-tone local oscillator signal by using a compressed sensing technology has an obvious advantage. However, a multi-tone local oscillator signal generated by using the compressed sensing technology has a harmonic in all multiplied frequencies of a fundamental frequency, that is, besides that a harmonic exists in a sub-band in which the multiband signal is located, a harmonic also exists in another sub-band that has no wanted signal. However, in a process of performing frequency mixing, signals in all sub-bands are moved to the baseband for aliasing. In this way, the multi-tone local oscillator signal moves noise and an interfering signal that are in the other sub-band to the baseband as well as moving all the narrowband signals in the multiband signal to the baseband. Aliasing of the wanted signal and the noise and the interfering signal enables a baseband signal obtained by frequency mixing to have a relatively low signal-to-noise ratio.